Our work carried out by support of PHS Research Grant EY00017 has clarified that the response to light of the vertebrate photoreceptors, both rods and cones, is of hyperpolarization irrespective of the mode, intensity and wavelength of the stimulating light, and that as the underlying mechanism the sodium channels in the outer segment membrane remain open in the dark and are closed by light. The response of the vertebrate photoreceptors was thus shown to be just backward in its ionic mechanism to the response of most receptors including most invertebrate photoreceptors in which the sodium channels are opened by light. The objectives of our research at this phase are to clarify the mechanism of information transmission between receptors and higher neural cells, with a final goal set to the elucidation of the mechanism of information processing in the vertebrate retina. Efforts towards the goal during the current year led to the following results: (a) A negative feed-back from horizontal cells to receptors was observed also in the carp, though never so dramatic as shown by Baylor et al. in the turtle. (b) Effects of glutamate and aspartate upon the two bipolar cell types were studied with the result that the off-center bipolar cell is depolarized by these amino acids, while the on-center bipolar cell is hyperpolarized, which suggested that the subsynaptic membranes of these two bipolar cell types react to the same chemicals in entirely opposite ways. Our study will continue along the same line.